Certain microsurgical interventions, for example, in hand surgery, cannot be executed by a single surgeon; they require the cooperation of at least one assistant. In this case, it is absolutely mandatory for the microscope of the assisting surgeon to be largely identical to the microscope of the responsible surgeon. In particular, it is necessary for both surgical microscopes to have the same stereo base and the same or at least approximately same viewing angle relative to the operation field.
U.S. Pat. Nos. 4,138,191 and 4,167,302 disclose surgical microscopes for two observers. It is a disadvantage in these surgical microscopes that either they do not permit the viewing angle between the two microscopes to be changed or, if they do, they require a complex arrangement of beam splitting and deflecting prisms.